ELLICOTT CITY, MD. — Kelli Myers slowly realized there was nothing left to save at Junk Girl, one of her two boutiques on historic Main Street in Ellicott City. Water had gushed into the basement of the store on July 30, 2016, during a devastating flood. That was where Myers had her office.

Her computers, business records, tax information, purchase orders, furniture and nearly everything else were destroyed. She threw damaged inventory in a pile in her back yard as she pondered what to do. Two months had passed when she called an old friend, a landlord who had a storefront open down the street in a historic building. It, too, had been damaged by the flood but not as badly as her store. She wanted to talk to her friend about renting 8120 Main St.

Her timing was uncanny.

“Come over now,” he told her. “We just found a cave.”

It was huge: about 12 feet wide and 8 feet tall at its center. It was carved into bedrock behind the building’s foundation and reinforced with crude masonry along the sides.

And nobody had any idea why it was there.

“It was jaw dropping,” said Myers, who reopened Junk Girl earlier this year. “It was like, ‘What is this?’ I was running up and down the street telling people about this.”

Ellicott City, local boosters like to say, is a town of mystery. Flood after flood has meant that the town has rebuilt more times than folks can remember. There’s a thriving ghost tour industry. A temperance-era preacher once called the town a “bootlegger’s paradise,” according to Howard County Historical Society Executive Director Shawn Gladden. The city also had a significant Quaker population in the mid-1800s that believed in abolition and was known for aiding runaway slaves.

Rescue workers survey the destruction caused by a flash flood along Main Street in Ellicott City last year. (Astrid Riecken for The Washington Post)

This city is used to floods — 1868, 1901, 1917, 1923, 1942, 1952, 1972 — but not like the one that hit last year.

The rushing waters of Tiber Creek and the Hudson River, engorged by six inches of rainfall in 30 minutes, killed two motorists in an event so extraordinary that the National Weather Service said it qualified as a thousand-year flood. Main Street became a raging river as people scrambled to the second floors of restaurants, businesses and homes. Cars piled on top of cars. Chunks of sidewalk vanished. Streets cratered, and 200 buildings were damaged. The Howard County executive described the wreckage as a “war zone.”

The cave was discovered as workmen repaired a house that had been built in 1840.

Given Ellicott City’s history, two theories emerged about its purpose, Gladden said. The first was that it was used to stash bootlegged whiskey during Prohibition. Main Street used to be lined with pharmacies, Gladden said, that “prescribed” alcohol if “patients” had a “cough.” Pharmacists needed a place to hide their extra supplies of the good stuff.

The second was that it was used as a stop on the Underground Railroad. The cave is large enough to fit quite a few people, and given the town’s Quaker ties, it seems plausible, Gladden said. Quakers played an outsize role in the abolitionist movement, and the three Ellicott brothers who purchased the land for the town were Pennsylvania Quakers. Historians, and unsuspecting homeowners, have found tunnels and trap doors in houses around town that have revealed what are believed to be Underground Railroad safe houses.

“Everything you’re going to hear at this point is all speculation because it’s so new,” Gladden said. “Nobody knew it was there.”

Then, earlier this week, Gladden and some research volunteers at the historical society set out to solve the mystery as the first anniversary of the flood approached.

And they found at least part of the answer.

Researchers located the property records for what was originally called the Samuel Powell House at the Maryland Historical Trust. Powell sold the building to George Smith in 1856 for $300. Smith sold it to William and Susan Brosius, who then sold it to Martin Rodey in 1868 for $800.

“Mr. Rodey ran a saloon here and a German beer garden in back. A deep cave, sixty to seventy feet from the top of the ground is in the back of the ground floor of this building in which they kept the beer,” the property record states. “A spring is also located here.”

Gladden cautions not to draw too much from these records. All that’s known is that the cave existed in 1868 and was used to store beer. But it could have been dug out previously and used for other purposes.

Rodey sold the Powell House in 1891. It changed hands again in 1915. Who knows what those owners, a Mr. and Mrs. Isaac H. Taylor, did with the cave?

No one does, Gladden said. And no one would have known about it without a thousand-year flood.